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Article

Performance in Multi-Joint Force-Plate Assessments in Male and Female CrossFit® Athletes

by
James R. Jowsey
1,*,
G. Gregory Haff
1,2,
Paul Comfort
1,2 and
Nicholas Joel Ripley
1
1
School of Health and Society, University of Salford, Salford M6 6PU, UK
2
School of Medical and Health Sciences, Edith Cowan University, Joondalup, WA 6027, Australia
*
Author to whom correspondence should be addressed.
Biomechanics 2025, 5(2), 35; https://doi.org/10.3390/biomechanics5020035
Submission received: 17 April 2025 / Revised: 5 May 2025 / Accepted: 15 May 2025 / Published: 1 June 2025
(This article belongs to the Section Sports Biomechanics)
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Versions Notes

Abstract

:
Background: CrossFit® aims to be equitable between both males and female athletes, supporting equal representation and equal prize money at international events. However, to date, limited information is known on CrossFit® athletes’ performance in the countermovement jump (CMJ), countermovement rebound jump (CMR-J), and isometric mid-thigh pull (IMTP) when assessed using force plates, and if there are any differences between sexes. Therefore, the purpose of the present study was to observe whether any sex-based differences and relationships exist between performance within these assessments. Methods: A total of CrossFit athletes (43 male = 32.8 ± 9.0 years; height 1.78 ± 0.06 m; mass = 92.4 ± 10.6 kg; and 31 female = 31.0 ± 7.6 years, height = 1.64 ± 0.05 m; mass = 68.8 ± 6.0 kg) completed three trials of CMJ, CMR-J and IMTP using portable dual-system force-plate sampling at 1000 Hz. Results: Moderate–large relationships were observed between CMJ, CMR-J and IMTP outcome measures (r = 0.396–0.809, p < 0.001). Males demonstrated small to moderately greater performance outcomes than females for CMJ height (males = 0.35 ± 0.08 m; females 0.30 ± 0.06 m, d = 0.73), CMR-J height (males = 0.32 ± 0.08 m; females = 0.30 ± 0.06 m, d = 0.39) and IMTP peak net force (males = 30.62 ± 10.01 N·kg−1; females = 27.49 ± 6.44 N·kg−1, d = 0.29). Conclusions: Maximal relative strength in CrossFit® athletes should be seen as imperative in both male and female athletes due to the meaningful relationship in ballistic and plyometric ability. Moreover, previous relationships with CrossFit® performance and the injury risk reduction benefits of improving strength provide further support. The descriptive data presented could be used by CrossFit® coaches to assess and compare the current performance of their own athletes in a battery of tests examining CMJ, CMR-J and IMTP, while also facilitating decisions upon prescription within training and competition.

1. Introduction

The physical qualities linked with CrossFit® performance include strength [1,2,3,4], local muscular endurance [4], aerobic performance (including VO2max) [1,5], and anaerobic capacity [1,5]. Furthermore, morphological factors including body fat percentage [6] and muscle size (e.g., vastus lateralis cross-sectional area) [5] have been linked with performance during the Murph benchmark workout and with final placing in the CrossFit® Open, respectively. However, Mangine and colleagues [7] highlight that there are inconsistent relationships between laboratory-based testing methods for measuring and predicting CrossFit® performance, which could suggest that the CrossFit® benchmark workouts may be more applicable than testing methods assessing a single physical quality for measuring and predicting CrossFit® performance. Despite this, it is important that the fundamental physical qualities which would underpin CrossFit® performance, such as lower limb strength and power for CrossFit® performance, are assessed in an isolated way so that coaches can identify potential weaknesses. The CrossFit® methodology incorporates powerlifting, weightlifting, jumping activities and metabolic conditioning and gymnastics [8], all of which require high levels of strength, power, and ballistic and plyometric capabilities [9,10,11,12]. Therefore, measuring these specific physical qualities in CrossFit® athletes provides valuable insights into the components that contribute to overall CrossFit® performance.
Muscular strength is a foundational physical quality underpinning weightlifting performance [10] and a range of sporting actions such as sprinting [13,14,15,16], jumping [17,18,19,20], and changing direction [21,22,23,24]. As CrossFit® workouts can incorporate any combination of these actions within a workout, strength is an important physical quality for CrossFit® performance [25]. Ultimately, higher levels of maximal strength are crucial as competitive level increases. Athletes reaching the CrossFit® Games finals have greater levels of strength than their lower-level counterparts, which has been observed within other sports [26,27,28,29]. Maximal strength has also been linked with increased CrossFit® performance in benchmark workouts including Fran [1,30], Grace [1] and CrossFit® Open performance [3,4,31]. Currently, maximal strength within CrossFit® populations has been assessed with either isokinetics for single-joint assessment [25], one repetition max (1-RM) assessments or via measuring peak force (PF) during an isometric mid-thigh pull (IMTP) [3,32,33,34]. The IMTP represents a viable alternative for testing in the CrossFit® environment due to several key advantages. This assessment is relatively quick to perform and provides detailed insights into an athlete’s force-generating capacities, including their force at early time points and rate of force development [20,24]. Additionally, the IMTP demonstrates strong relationships with measures of athletic performance while being less fatiguing than traditional 1-RM testing [35]. Despite maximal single-effort assessments potentially not being representative of CrossFit® competitive events, improvements in maximal capacity will make any submaximal effort of a lower relative exertion [11]. Suchomel et al. [11] also identified that there is no substitute for improved muscular strength to improve both general and sport-specific skills of athletes, while also reducing the risk of injury.
The ability to express high levels of muscular power (i.e., the product of force and velocity, or work carried out over time) is considered a key determinant of athletic performance [36] and is crucial for rapid acceleration of mass [10,36]. CrossFit® success often depends on completing either a maximum number of repetitions within a fixed time or a set number of repetitions in the fastest time possible. At the 2018 CrossFit® Games, athletes performed a five-repetition clean and jerk ladder, with increasing loads (males = 143, 147, 152, 154, and 156 kg; females = 93, 95, 97.5, 100, and 102 kg) as quickly as possible. Events like the clean and jerk ladder highlight the importance of lower body muscle maximal strength and power, which is commonly assessed through the countermovement jump (CMJ), with jump height (JH) serving as a proxy measure [36,37]. The CMJ utilizes the stretch-shortening cycle (SSC) (i.e., the sequential eccentric lengthening immediately followed by a concentric shortening of muscle fibres) [38], a mechanism prevalent in sports movements involving running, jumping, and rapid changes in velocity [38]. Furthermore, as CrossFit® sessions can include a variety of tasks that require high levels of SSC performance including running tasks (over varied distances), skipping (double-unders, triple-unders and crossovers) or box jumps to heights ranging from 0.51 to 1.07 m. The ability of CrossFit® athletes to perform fast SSC (<250 ms) has been assessed using drop jumps with box heights ranging from 0.20 to 0.70 m [2,30,34], with drop jump ability shown to correlate with CrossFit® Open performance [5]. However, the actual fall height and box height can differ when performing the drop jump, with reported mean drop heights 10% and 14% lower than a box height of 0.30 m and 0.40 m, respectively, [39], impacting touchdown velocity [40]. Xu and colleagues [40] therefore propose the countermovement rebound jump (CMR-J) as an alternative test for fast SSC ability. As the initial JH (fall height for the rebound jump) can be accurately determined, the test is self-limiting as it is performed from a height that the participant can jump to and therefore, better aligns with their force-producing capabilities. Interestingly, recent updates to CrossFit® performance have included competitions selectively altering repeated box jump standards, incorporating step down rather than jump and rebound. Although this change has likely been performed to reduce the risk of injury, it does remove the larger rebound jump requirement potentially limiting the specificity to the CMR-J. However, as many actions performed in CrossFit® such as skipping, with various ropes and intensities (double vs. triple unders), as well as sprinting and running actions, require the Achilles tendon to effectively perform elastic amplification of force, presenting the utility of the CMR-J [41], despite potentially lacking specificity to CrossFit®.
Despite the literature relating force-generating characteristics to CrossFit® performance, there are limited literature observing whether any sex differences exist between CrossFit® athletes, especially as CrossFit® aims to be equitable between both males and female athletes, supporting equal representation and equal prize money at international events. Moreover, there are limited observations on fast SSC capabilities within CrossFit® athletes, despite the sports increasing use of skipping tasks and box jump from higher heights. Therefore, the purpose of the present study was to determine if any sex differences exist in outcome measures in IMTP, CMJ and CMR-J from male and female CrossFit® athletes. It was hypothesized that males would have improved maximal strength, ballistic and plyometric qualities. It was also aimed to determine the relationship between outcome measures in IMTP, CMJ and CMR-J in CrossFit® athletes to potentially support training goals. It was hypothesized there would be positive relationships between IMTP, CMJ and CMR-J outcome measures. A secondary aim of the present study was to provide descriptive data for the IMTP, CMJ and CMR-J from male and female CrossFit® athletes.

2. Materials and Methods

2.1. Experimental Setup

An observational study design was used where athletes performed three to five maximal repetitions with one minute rest between trials of the CMJ, followed by the CMR-J and subsequently the IMTP on a single test occasion. All testing was conducted between June and November 2023, encompassing what would be representative of a period of off-season, pre-season and in-season training for CrossFit® athletes, depending on their progression within the competition CrossFit® season (i.e., Open, quarter finals, semi-finals and Games). To observe if relationships exist between outcome measures, including jump height and relative peak force, for the CMJ, CMR-J and IMTP in CrossFit® athletes, a priori sample size estimation indicated a required sample of n = 14 was required based on an effect size r = 0.558, alpha error probability = 0.05 and statistical power = 0.80 based on the observed relationships between IMTP and CMJ performance [17]. To determine if any sex differences exist between key outcome measures, including jump height and relative peak force, for the CMJ, CMR-J and IMTP for CrossFit® athletes, a priori sample size estimation indicated a required sample of n = 36 (18 per group) was required based on an effect size g = 0.87, alpha error probability = 0.05 and statistical power = 0.80 based on the observed difference between sexes in the IMTP [42].

2.2. Participants

Seventy-four CrossFit® athletes volunteered to participate in this study ranging from trained participants, whereby regular training is performed (~3 times per week), competing at a local level with the purpose to compete, to elite international-level participants who compete at the international level between the top 4 and 300 participants in the world rankings, with highly proficient skills and maximal training allowing them to compete at competitive levels such as the semi-finals and Games; these classifications are based on the study by McKay et al. [43]. A total of 43 males (33.0 ± 9.0 years, height = 1.78 ± 0.06 m; mass = 92.4 ± 10.6 kg) and 31 females (31.0 ± 8.0 years, height = 1.64 ± 0.05 m; mass = 68.8 ± 6.0 kg) participated in the current study. Prior to testing, all participants provided written informed consent with parental consent obtained from all participants under the age of 18 years (n = 2). The study was conducted in accordance with the Declaration of Helsinki 2013 and approved by the University of Salford’s Institutional Ethics Committee (application ID 11926). All participants were required to refrain from physical activity 48 h prior to testing. On arriving at the gym, participants performed a standardized bodyweight warm-up incorporating squats, lunges, calf raises, leg swings, submaximal vertical jumps and submaximal repeated jumps. This was followed by 1 set of 5 repetitions of a dynamic mid-thigh clean pull with the empty bar and one set of a dynamic mid-thigh clean pull, separated by 1 min rest at 30 and 50% of the participant’s 1-RM power clean.

2.3. Procedures

Participants performed three to five CMJs and CMR-Js, interspersed with 60 s rest. For both jump tests participants were instructed to perform the CMJ to a self-selected squat depth and to “jump as fast and as high as possible”. The verbal cue to “jump as fast” was used to ensure that both the countermovement and propulsion phases were performed as quickly as possible as this can exert an influence on force–time characteristics during jumping tasks [44]. All jumps were performed on dual force plates (Hawkin Dynamics, Westbrook, ME, USA) that were sampled at 1000 Hz, with a foam surround placed around the force plates.
All jumps were performed with arms akimbo (i.e., hands on hips) to eliminate the effect arm swing has on force–time variables [45]. Prior to commencing the CMR-J, participants were instructed to perform a CMJ based on the same instructions, and then to immediately perform a rebound jump as “fast as possible”, aiming to minimize ground contact time (GCT). CMJ trials were excluded if the participants’ arms left the hips or there were consistent increases in jump height observed. CMR-J trials were excluded if the akimbo position was not maintained or if the GCT was >250 ms [46]. If an athlete was not capable of meeting these requirements, further trials were taken until a maximum of five were performed. Reactive strength index (RSI) and modified RSI were calculated via dividing jump height via GCT, or time to take off, within the CMR-J and CMJ, respectively.
Vertical ground reaction force was low-pass-filtered at 50 Hz in accordance with recommendations [47]. The onset of movement was identified when the force decreased by >5 standard deviations of body weight during the initial one second period of quiet standing, while take-off was determined when the vertical force dropped below 25 N during the propulsive phase. All metrics were calculated automatically by the force plate proprietary software [48].
The IMTP was performed using standardized protocols while using an adjustable rig and fixed bar (Absolute Performance, Cardiff, Wales) that was coupled with force-plate sampling at 1000 Hz (Hawkin Dynamics, Westbrook, ME, USA) (Figure 1) [49]. Specifically, the participant adopted a self-selected position that replicated the start of the 2nd pull of the clean, resulting in knee and hip joint angles of 125–145° and 140–150°, respectively. All participants used a clean grip and lifting straps to hold onto an immovable bar. Participants were instructed to remove “slack” from the body without creating any pre-tension on the bar so that a “quiet standing” period could be established, allowing a stable force baseline to be quantified. All participants were instructed to “push into the ground as hard and as fast as they can” on the count of “3,2,1 PUSH”. The 3 × 3 s warm-up trials performed at 50, 75 and 90% rate of perceived exertion, respectively, were used to familiarize the participants with the IMTP. Straps were used during the warm-up trials to offer a familiarization, as straps are not permitted in competition and mixed experience with using straps within the cohort. Maximal effort trials lasted between 4 and 6 s in duration with strong verbal encouragement provided, with 1 min rest between trials, a threshold was applied to the IMTP, where further trials were performed if PF changed by >250 N or 5% [49].
The IMTP force–time data were analyzed using an onset threshold of an increase in force >3 SDs of the force during the one second period of quiet standing, with the highest force achieved identified as PF. The system mass determined from the CMJ was subtracted from this value to ensure that only net PF was reported. Relative metrics for IMTP were calculating using the body mass observed from the CMJ.

2.4. Statistical Analyses

Statistical analyses were conducted using Jamovi (Version 2.3, Computer Software. Retrieved from https://www.jamovi.org, Sydney, Australia). Data are presented as the mean ± standard deviation (SD). Normality was verified using the Shapiro–Wilk’s test in addition to absolute z-test. A “Z-Test” was conducted to assess normality using skewness and kurtosis [50]. This was carried out by dividing the skew values or “excess” kurtosis by their standard errors [50]. For smaller ‘small-sized’ (N < 50) samples, an absolute z-value of ≥1.96 (p < 0.05) was described to conclude the distribution of the data in this sample as non-normal [50].
The a priori alpha level was set at <0.05. Absolute reliability was calculated using coefficient of variance (CV%) based on the sample SD and 95% upper bound confidence interval (CI95), interpreted as <5.00%, 5.00–9.99%, 10.00–14.99% and >15% as excellent, good, moderate and poor, respectively, [51]. Relative reliability was assessed using two-way absolute agreement intraclass correlation coefficients (ICC), ICC values were interpreted based on the lower bound CI (ICC; poor ≤ 0.49, moderate 0.50–0.74, good 0.75–0.89 and excellent >0.90) [52].
To determine if a relationship exists between outcome measures (jump height and relative peak force) for the CMJ, CMR-J and IMTP, Pearson’s correlation coefficient was run with 95% confidence intervals, with calculation of the coefficient of determination (R2). Pearson’s correlation coefficients were interpreted as follows: ≤0.10, trivial; 0.11–0.30, small; 0.31–0.50, moderate; 0.51–0.70, large; 0.71–0.90, very large; >0.90, almost perfect [53]. To observe if there were differences in outcome measures (jump height and relative peak force) for the CMJ, CMR-J and IMTP between sexes, a series of independent sample t-tests were run with Cohen’s d effect sizes as a measure of magnitude; effect sizes were interpreted as follows: <0.20, trivial; 0.20–0.59, small; 0.60–1.19, moderate; ≥1.20, large [53].
Descriptive benchmarks, T-score performance bands and application of the traffic light system were recorded using Microsoft Excel (Microsoft Corp., Redmond, WA, USA) in accordance with the work of McMahon et al. [37]. The participants’ mean score of three recorded trials was used to calculate their Z- and T-scores using Equations (1) and (2), respectively.
Equation (1). Z-Score equation.
Z Score = (Mean Athlete score − Group mean) ÷ Group standard deviation
Equation (2). T-Score equation.
T-score = (Z-score × 10) + 50
The Z-score determines how many SDs above or below the group mean value an individual’s score is running from −3 to +3 at 0.5 confidence intervals. T-scores were calculated to allow for athletes to be ranked from 1 to 100 in the following performance bands: poor, below average, average, above average, good, very good and excellent [37]. A traffic light system approach applied to the T-scores to compliment the allocated qualitative descriptions and therefore, simplifying the interpretation of the data to the end user, i.e., athlete or coach [54].

3. Results

Absolute z-values, calculated by dividing the skew values or “excess” kurtosis by their standard errors, equalled between 0.048 and 0.898 for the male sample and between 1.030 and 1.778 for the female sample for the CMJ, CMR-J and IMTP metrics. These results highlight that the data from the present study are normally distributed, enabling the creation of descriptive benchmarks.
Excellent absolute and relative reliability were observed for CMJ (JH, jump momentum (JM)), CMR-J (CMJ height) and IMTP (PF) (Table 1, Table 2 and Table 3). Additionally, excellent absolute and good relative reliability were observed for CMR-J rebound height (Table 2). Good absolute and moderate-to-good relative reliability were observed for countermovement depth (CMD), while poor-to-moderate relative reliability was observed for CMJ (time to take-off [TTTO]) and CMR-J (GCT) (Table 1 and Table 2).
Pearson’s correlations revealed moderate-to-large significant relationships (r = 0.396–0.809, p < 0.001) between CMJ height, CMR-J height and IMTP relative peak force (Figure 2).
A moderate difference was observed between sexes for CMJ JH (d [95% CI] = 0.73 [0.25–1.20], p = 0.003), with a large difference in CMJ momentum (d [95% CI] = 2.51 [1.89–3.09], p < 0.001). Trivial–small differences were observed between sexes for CMR-J rebound height (d [95% CI] = 0.39 [−0.07–0.86], p = 0.102), CMR-J RSI (d [95% CI] = 0.01 [−0.47–0.46], p = 0.976) and CMR-J GCT (d [95% CI] = 0.19 [−0.27–0.66], p = 0.144). There was a small difference in IMTP relative net peak force (d [95% CI] = 0.29 [−0.17–0.76], p = 0.217), with a small difference observed in IMTP relative net force at 250 ms (d [95% CI] = 0.42 [0.28–1.23], p = 0.001).
Sex-specific descriptive benchmarks (based on the T-score bands) for relative net PF and PF at 250 ms, CMJ JH and relative peak propulsive power and rebound JH are presented in Figure 3.

4. Discussion

The purpose of this study was to determine whether any sex differences exist in outcome measures in IMTP, CMJ and CMR-J from male and female CrossFit® athletes, and observe if any relationship existed between the outcome measures. In agreement with the hypotheses, moderate-to-large relationships were observed between outcome measures in IMTP, CMJ and CMR-J, with trivial-to-large differences between sexes in the outcome measures. We also aimed to provide descriptive data for the CMJ, CMR-J and IMTP using force plates for male and female CrossFit® athletes. It is important to note that the relative reliability (ICC) is crucial for establishing data sets [42]. Within the present study, excellent within-session relative reliability was observed for CMJ JH, IMTP PF, with good relative reliability observed for CMR-J rebound JH for both males and females (Table 1). The GCT for the rebound portion of the CMR-J had poor-to-moderate relative reliability for both females and males (Table 1). The descriptive data presented in this study for CMJ, CMR-J and IMTP may be used by CrossFit® coaches and athletes to facilitate the decision-making process for future training interventions.
Moderate differences in CMJ JH and jump momentum were observed between males and females. This highlights the fact that male CrossFit® athletes accelerated a greater mass to achieve the moderately higher JH, thus producing greater relative net propulsive impulse. Ballistic capabilities have previously been assessed in CrossFit® athletes: the males’ range is 0.14–0.47 m; the females’ range is 0.17–0.38 m [2,30,55]. Previous literature have utilized different methods of assessment of CMJ JH [32,34] and CMJ performance via using arm swing [2,30,55]. Both factors can lead to inflated JH values, as the use of flight time overestimates JH when compared to the impulse-momentum method (i.e., determining JH via velocity of centre of mass at take-off) [56,57]. Similarly, the use of arm swing during the CMJ results in greater JH via increased propulsive impulse [2,30,55]. The authors of the present study wanted to ensure consistency between participants and to isolate the physical quality of lower limb ballistic performance [2,30]. Sauvé et al. [55] reported greater JH for both male and female CrossFit® athletes (males = 0.50 ± 0.03 m; females = 0.40 ± 0.04 m) using the proposed impulse-momentum method; however, all CrossFit® athletes included within the study by Sauvé et al. [55] were extremely high-level (in the top 15 within the CrossFit® Open or participated within the CrossFit® games) potentially explaining the greater JH. The present study included a mixed cohort who initially started at the competitive calendar at the CrossFit® Open to provide descriptive data for this event. It is likely that more successful athletes (i.e., further through the CrossFit® Open to the quarterfinals, semi-finals and games) will likely have better-developed physical qualities. This notion is supported by the lower average JH reported by Garcia Fernandez et al. [58] (male and females = 0.28 ± 0.08 m), Conde et al. [32] (females = 0.19 ± 0.06 m), and Párragga-Montilla et al. [34] (females 0.25 ± 0.04 m), with the latter reporting similar JH within male CrossFit® athletes to those observed within the present study (0.35 ± 0.06 m). Párragga-Montilla et al. [34] included local “box” (CrossFit® gym) members and physically active CrossFit® practitioners, while participants in Garcia Fernandez et al.’s work [58] were described as non-elite. Comparatively, the male and female participants who participated within the present study ranged from the local “box” members to highly competitive national and international athletes, potentially explaining the increased JH observed in this study, although this needs further investigation.
Male athletes possessed a greater relative net peak force in comparison to female athletes to a small magnitude; however, female athletes produced a greater relative net force at 250 ms to a small magnitude. This is consistent with previous literature where female team sports produced a greater relative net force at 250 ms in comparison to male team sport athletes, albeit to a trivial magnitude [42]. This larger difference observed within the present study for rapid force and peak force could be explained by the greater familiarity with weightlifting type movements athletes are exposed to within CrossFit® training, in comparison to team sport athletes. The gross PF from the IMTP test in the present study are higher than those presented in the existing literature [5,25,33]. However, what is unknown from the literature is whether the reported values are gross or net PF, i.e., do or do not include body mass. Hodžic et al. [25] reported average PF values for elite and well-trained males (elite = 2894 N; well-trained 3184 N) and females (elite = 2292 N; well-trained 2031 N). Mangine and colleagues [5,33] reported lower PF values in two separate studies including different cohorts, including high performing athletes (regional/semi-final and games athletes) demonstrating average PF values of 1746 ± 473 N. If the reported values from the scientific literature are gross PF, they potentially indicate methodological limitations, such as the omission of weightlifting straps as part of the methods; however, if they are net PF they are comparable and, in the case of Hodžic et al. [25], exceed the values presented within the present study. This is an important consideration as the standardized IMTP testing procedures outlined by Comfort et al. [49] recommend the use of weightlifting straps in order to remove grip as a limiting factor, allowing for a more accurate assessment of lower body force production. Future studies that investigate the IMTP within CrossFit® populations should ensure that standardized IMTP testing procedures are followed with clear methodological reporting (i.e., the use of weightlifting straps and gross or net PF).
The relative reliability observed in this study for the CMR-J rebound JH and GCT is lower than the good reliability reported by Xu and colleagues [40] for both jump height (ICC (95% CI) = 0.93 (0.87–0.97)) and rebound contact time (ICC (95% CI) = 0.94 (0.89–0.97)). However, the rebound GCTs reported by Xu et al. [40] were far longer than those observed within the present study for both males and females, 350.0 ± 120.0 s vs. 261.03 ± 75.14 ms and 247.56 ± 63.23 ms, respectively. Tapley et al. [59] has suggested that this test does not provide a valid representation of the fast SSC. It is likely that the lack of validity for fast SSC is a function of the inability to achieve a GCT ≤ 250 ms during test, which could be a function of poor coaching (i.e., not using appropriate cues) or not having strict trial exclusion criteria. The present study excluded trials that exceeded the 250 ms, with participants performing a maximum of five trials. Despite this, the average GCT for males still exceeded 250 ms, albeit being 11 ms greater than the threshold. The lower reliability observed within the present study could potentially be due to the lack of familiarization being provided for the CMR-J test. Therefore, future research in CrossFit® populations should look to add 1–2 familiarization sessions prior to performing CMR-J or alternative methods of assessing fast SSC.
Interestingly, female athletes within the present study had a lower mean GCT < 250 ms which would be considered a fast SSC action < 250 ms [38,45], in comparison to male athletes, albeit only trivial in magnitude,. The greater elastic capabilities observed within female CrossFit® athletes is supported by previous literature identifying that females can utilize a greater portion of stored elastic energy during jumping tasks while male athletes retain greater rebound jump outcome [60]. CrossFit® programming incorporates various jumping activities, with box jumps typically ranging from 0.51 to 1.07 m in height. Therefore, CrossFit® athletes will tend to adopt a more compliant jumping strategy with reduced muscle-tendon stiffness. This strategy increases vertical net propulsive impulse and take-off velocity to achieve the required jump height [38]. However, this emphasis on higher box jumps may inadvertently limit the development of fast SSC capabilities in CrossFit® athletes, as the movement pattern encourages slower, more compliant jumping strategies rather than explosive, fast SSC movements. Although the CMR-J may lack specificity to CrossFit® activities such as running and skipping, the assessment of the underpinning elastic qualities would still be of interest to ensure energy efficiency during these tasks and events.
The importance of fast SSC ability has been previously established in CrossFit® athletes, where drop jump performance (RSI), strongly correlates with CrossFit® Open performance [5]; moreover, it could be hypothesized that the elastic qualities of the Achilles tendon assist CrossFit® athletes in expressing high force at high velocities under fatigue, such as ascending weightlifting events; however, this needs further investigation. The positive relationship between fast SSC ability and CrossFit® Open performance, and the hypothesized relationship between the elastic qualities of the Achilles tendon and expression of high force at high velocities under fatigue highlight that the fast SSC capability of athletes may be a useful tool informing training decisions to improve overall CrossFit® performance. Although correlation does not equal causation, decreasing the time taken to perform a plyometric or the transition phase within the weightlifting exercises task will result in enhanced stretch augmentation that improves the rate of performing work [61], while simultaneously improving the economy of jumping-based activities, via the storage and release of elastic energy which reduces the energy required to perform the expected work [38]. Comparing CrossFit® athletes with strength-matched individuals from other sports such as gymnastics and combat sports could help to determine whether CrossFit® athletes possess under-developed fast SSC capabilities.
Laboratory tests offer greater diagnostic ability; however, several researchers have suggested that field-based testing (i.e., CrossFit® benchmark tests) may be more appropriate for measuring CrossFit® performance, as previous CrossFit® experience has been linked to increased performance within the CrossFit® Open [7]. However, different physical qualities including strength [1,30,62] and aerobic performance (i.e., VO2max) [5,62] have been reported to underpin performance in CrossFit® workouts. As CrossFit® workouts could comprise a single modality, such as a 5 km run or a 1-RM clean and jerk, having an increased VO2max or greater strength capabilities likely underpins success in these activities. Subsequently, laboratory-based markers of individual physical qualities should be considered to be equally important as the field-based ‘benchmark’ CrossFit® tests. Therefore, in addition to assessing field-based CrossFit® benchmark tests, practitioners and researchers should continue to assess the lower body force-generating capabilities including ballistic (CMJ), reactive (CMR-J), and maximal isometric (IMTP) characteristics as well as the aerobic performance (i.e., VO2max) capacities of CrossFit® athletes. Ultimately, the combination of these assessments could be used to develop a CrossFit®-specific Total Score of Athleticism [63], which could aid in the identification of an athlete’s strengths and weaknesses. This information could then be utilized to guide training decisions.
The present study is not without its limitations as the participants were drawn from a CrossFit® population with mixed abilities and performed at different locations and with athletes who participate in different amounts of training. For example, some participants only attended three to five CrossFit® classes (i.e., 60 min per session) per week, whilst higher-level, competitive participants trained 2–3 h per day, at least 5 days per week. Therefore, the descriptive data and sex differences only provide a global representation of athlete capacity and are not representative of the spectrum of novice-to-elite-level CrossFit® athletes and should be interpreted with caution. However, as all participants competed within the CrossFit® Open, which is still reliant on key physical qualities such as strength, ballistic and reactive ability, it is likely these physical qualities would have some relevance to the progression within the CrossFit® competitive calendar. However, this is a standardized starting point for all participants entering CrossFit® competition, indicating the utility of the benchmarks provided. Further research should look to examine whether performance in competitions (Open, semi-finals and Games) increases if a higher ranking is achieved within the force-plate assessments within the present study. Therefore, the descriptive data provided should also be interpreted with caution, especially as they do not provide normative data for practitioners as they do not differentiate between age groups or competition level within the included cohort. However, we hope the descriptive data and associated benchmarks can aid in identifying training needs for athletes. Although it was advised that athletes should refrain from intense activity in the 48 h prior to testing, it is unknown whether this was adhered to; therefore, the presented values may not represent the CrossFit® athlete’s best performances. However, as CrossFit® challenges athletes to perform 1-RM max testing in the middle of a competition weekend, performing these maximal effort force-plate tests with a level of fatigue is specific to the requirements of the sport, and therefore provides ecologically valid data. Within CrossFit® competition athletes are not permitted to use straps; therefore, they rarely use straps within training highlighting a potential for lack of familiarity of using straps within the IMTP, reducing the accuracy of the lower limb maximal strength. However, using a familiarity protocol during the warm-up trials and the standardized procedures [49] aimed to reduce this effect, but it may still lack accuracy.

5. Conclusions

Meaningful relationships between outcome measures for the CMJ, CMR-J and IMTP highlight the requirement for CrossFit® athletes to develop all physical qualities that could underpin CrossFit® Open performance [3,4,31], specifically ballistic, plyometric and maximal strength characteristics. Moreover, when maximal strength is ratio-scaled to body mass, only a small difference is observed between sexes for peak and force at 250 ms. This highlights the necessity of observing maximal strength in absolute and relative conditions for CrossFit® athletes due to the increased loads prescribed for male athletes, as well as the previously identified associations with ballistic and plyometric ability and CrossFit® Open performance [3,4,31]. However, caution should be taken as correlation does not equal causation, and further investigation is warranted. Training should look to develop maximal strength relative to body mass, as relative force dictates acceleration via Newton’s second law (force = mass × acceleration). Relative strength also dictates rapid force-generating capacity, which has implications on velocity as relative impulse (impulse = force × time) determines velocity, with the acceleration and velocity imparted onto the athlete’s own mass or an external mass, such as a barbell, dumbbell or sled, being crucial for competition success. The descriptive data presented in this study may be used by CrossFit® coaches to assess and compare the current performance of their own athletes in a battery of tests, including the CMJ, CMR-J and IMTP. The performance bands provided could be used to facilitate the decision-making process for CrossFit® coaches and athletes for future training interventions and subsequently, monitoring the progress of training, they do need to be interpreted with caution due to the mixed cohort and sample size.

Author Contributions

Conceptualization, J.R.J. and N.J.R.; methodology, J.R.J.; investigation, J.R.J.; writing—original draft preparation, J.R.J.; writing—review and editing, J.R.J., G.G.H., P.C. and N.J.R.; visualization, J.R.J.; supervision, N.J.R.; project administration, J.R.J. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

The study was conducted in accordance with the Declaration of Helsinki and approved by the Institutional Review Board of the University of Salford (protocol code 11926 and 28 April 2023).

Informed Consent Statement

Informed consent was obtained from all subjects involved in the study. Written informed consent has been obtained from the patient(s) to publish this paper.

Data Availability Statement

The raw data supporting the conclusions of this article will be made available by the authors upon request.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
CMJCounter Movement Jump
CMR-JCounter Movement Rebound Jump
IMTPIsometric Mid-Thigh Pull
RSIReactive Strength Index
mRSIModified Reactive Strength index

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Biomechanics 05 00035 g001
Figure 1. Isometric mid-thigh pull setup position, replicating the start of the 2nd pull of the clean.
Figure 1. Isometric mid-thigh pull setup position, replicating the start of the 2nd pull of the clean.
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Figure 2. Scatter plots with linear line of best fit (blue line) and 95% confidence intervals (grey shaded area) between (A) CMJ height and CMR-J rebound height, (B) IMTP relative net peak force and CMJ height and (C) IMTP relative net peak force and CMR-J rebound height with r and R2.
Figure 2. Scatter plots with linear line of best fit (blue line) and 95% confidence intervals (grey shaded area) between (A) CMJ height and CMR-J rebound height, (B) IMTP relative net peak force and CMJ height and (C) IMTP relative net peak force and CMR-J rebound height with r and R2.
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Figure 3. Descriptive data for male and female CrossFit® athletes with T-score bands presented in a traffic light system for force-generating characteristics.
Figure 3. Descriptive data for male and female CrossFit® athletes with T-score bands presented in a traffic light system for force-generating characteristics.
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Table 1. Within-session reliability and group mean and standard deviation for CMJ performance variables.
Table 1. Within-session reliability and group mean and standard deviation for CMJ performance variables.
Countermovement Jump
Performance VariableCV% (95% CI)ICC (95% CI)Group Mean (SD)
MaleFemaleMaleFemaleMaleFemale
CMJ Height (m)2.91
(1.72–4.10)		2.21
(1.31–3.12)		0.962
(0.943–0.976)		0.946
(0.913–0.968)		0.35 (0.08)0.30 (0.06)
CMJ Momentum
(kg·m·s−1)		1.99
(1.59–2.40)		1.14
(0.68–1.61)		0.950
(0.924–0.968)		0.956
(0.922–0.976)		237.07 (35.85)164.77 (19.13)
CMJ Depth (m)4.32
(2.56–6.09)		6.81
(4.03–9.59)		0.877
(0.819–0.92)		0.791
(0.686–0.871)		0.21 (0.06)0.19 (0.05)
Time to take-off (s)5.53
(3.90–7.15)		4.21
(3.31–6.11)		0.559
(0.415–0.690)		0.78
(0.670–0.864)		0.59 (0.10)0.55 (0.11)
mRSI3.32
(2.38–4.27)		3.48
(2.28–4.68)		0.780
(0.855–0.687)		0.845
(0.761–0.906)		0.59 (0.13)0.55 (0.13)
Relative average propulsive force (N·kg−1)4.04
(2.02–6.06)		3.25
(1.74–5.76)		0.873
(0.813–0.918)		0.837
(0.751–0.901)		244.46 (21.36)238.28 (25.43)
Relative peak propulsive power (W·kg−1)4.74
(3.44–6.75)		6.37
(4.22–8.52)		0.862
(0.842–0.876)		0.847
(0.815–0.869)		57.47 (8.23)51.83 (7.52)
CV% = coefficient of variation percentage, ICC = intraclass correlation coefficient, 95% CI = 95% confidence intervals, SD = standard deviation, CMJ = countermovement jump, mRSI = modified reactive strength index.
Table 2. Within-session reliability and group mean and standard deviation for CMR-J performance variables.
Table 2. Within-session reliability and group mean and standard deviation for CMR-J performance variables.
Countermovement Rebound Jump
Performance VariableCV% (95% CI)ICC (95% CI)Group Mean (SD)
MaleFemaleMaleFemaleMaleFemale
CMJ Height (m)3.08
(3.23–4.92)		3.62
(2.37–4.87)		0.948
(0.922–0.967)		0.844
(0.759–0.906)		0.33
(0.08)		0.29
(0.06)
RJ Height (m)5.93
(0.55–1.31)		4.46
(3.86–5.05)		0.894
(0.844–0.932)		0.963
(0.940–0.979)		0.32
(0.08)		0.30
(0.06)
RJ Ground contact Time (ms)3.19
(1.89–4.50)		4.28
(1.35–3.22)		0.736
(0.630–0.823)		0.620
(0.461–0.755)		261.03 (75.14)247.56 (63.23)
Rebound RSI6.91
(5.72–9.09)		5.80
(4.06–6.53)		0.752
(0.650–0.835)		0.775
(0.661–0.862)		2.05
(0.53)		2.03
(0.47)
CV% = coefficient of variation percentage, ICC = intraclass correlation coefficient, 95% CI = 95% confidence intervals, SD = standard deviation, CMJ = countermovement jump, RJ = rebound jump, RSI = reactive strength index.
Table 3. Within-session reliability and group mean and standard deviation for IMTP performance variables.
Table 3. Within-session reliability and group mean and standard deviation for IMTP performance variables.
Isometric Mid-Thigh Pull
Performance VariableCV% (95% CI)ICC (95% CI)Group Mean (SD)
MaleFemaleMaleFemaleMaleFemale
Gross Peak Force (N)3.69
(1.41–4.97)		3.50
(1.30–5.71)		0.977
(0.964–0.985)		0.950
(0.920–0.971)		3695.80 (787.46)2548.99 (425.12)
Net Peak Force (N)3.05
(1.62–4.47)		3.68
(1.40–5.96)		0.832
(0.757–0.890)		0.904
(0.849–0.943)		2785.42 (802.05)1875.50 (418.57)
Relative Gross Peak Force
(N·kg−1)		2.49
(1.88–3.09)		2.95
(1.15–3.74)		0.729
(0.620–0.818)		0.781
(0.672–0.864)		40.43 (10.01)37.30
(6.44)
Relative Net Peak Force
(N·kg−1)		3.01
(1.78–4.25)		3.38
(2.82–4.94)		0.940
(0.909–0.962)		0.780
(0.672–0.864)		30.62 (10.01)27.49
(6.44)
Net Peak Force at 250 ms (N)5.38
(3.41–7.85)		4.44
(3.04–5.85)		0.680
(0.559–0.783)		0.701
(0.566–0.811)		1499.46 (35.63)1250.91 (179.81)
Relative Net Peak Force 250 ms
(N·kg−1)		4.91
(3.54–6.28)		4.97
(3.76–7.18)		0.717
(0.605–0.809)		0.674
(0.531–0.792)		15.76 (5.85)18.33
(6.20)
CV% = coefficient of variation percentage, ICC = intraclass correlation coefficient, 95% CI = 95% confidence intervals, SD = standard deviation, IMTP = isometric mid-thigh pull.
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Jowsey, J.R.; Haff, G.G.; Comfort, P.; Ripley, N.J. Performance in Multi-Joint Force-Plate Assessments in Male and Female CrossFit® Athletes. Biomechanics 2025, 5, 35. https://doi.org/10.3390/biomechanics5020035

AMA Style

Jowsey JR, Haff GG, Comfort P, Ripley NJ. Performance in Multi-Joint Force-Plate Assessments in Male and Female CrossFit® Athletes. Biomechanics. 2025; 5(2):35. https://doi.org/10.3390/biomechanics5020035

Chicago/Turabian Style

Jowsey, James R., G. Gregory Haff, Paul Comfort, and Nicholas Joel Ripley. 2025. "Performance in Multi-Joint Force-Plate Assessments in Male and Female CrossFit® Athletes" Biomechanics 5, no. 2: 35. https://doi.org/10.3390/biomechanics5020035

APA Style

Jowsey, J. R., Haff, G. G., Comfort, P., & Ripley, N. J. (2025). Performance in Multi-Joint Force-Plate Assessments in Male and Female CrossFit® Athletes. Biomechanics, 5(2), 35. https://doi.org/10.3390/biomechanics5020035

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